Caltrans Was Warned on Vulnerable Design : Safety: An official also admits existing technology might have saved the Nimitz Freeway from collapse.

A top Caltrans official acknowledged Friday that the department had been warned 2 1/2 months before an earthquake destroyed the Nimitz Freeway that structures with similar designs in the Bay Area were vulnerable to quakes.

James E. Roberts, Caltrans’ chief of structures, also acknowledged for the first time that the double-decker freeway in Oakland that collapsed Oct. 17, killing at least 39 people, might have been saved with existing technology. But he added that the strengthening methods would have been temporary and not “pretty.”

“Temporarily, we can do that,” Roberts said. “To say that it would have prevented it from going down, certainly there would have been a higher level of assurance.”

Roberts, speaking at a news conference, seemed to back away somewhat from previous statements that no technology exists that could have provided earthquake strengthening to the double-column support system used on the Nimitz. He maintained that more research is needed to develop the technology to strengthen such double-column bridges.

It was also the first time that he acknowledged knowing before the Oct. 17 earthquake that a design system similar to the one used to support the Nimitz was vulnerable during a quake.

Gov. George Deukmejian has said that he would have closed any freeway in California had he been warned that it was unsafe.

The governor’s office, which has repeatedly said that Deukmejian received no such warning, had no comment Friday on Roberts’ disclosure.

Roberts said he attended an Aug. 1 meeting with four engineers that Caltrans hired to review a plan to strengthen the system tying together roadbed sections of the Embarcadero Freeway in San Francisco, a structure with a design similar to the Nimitz’s.

During the course of their review, Roberts said, the engineers discovered that a method used to connect some of the Embarcadero’s supporting columns made the freeway vulnerable to an earthquake.

Three weeks later, on Aug. 21, James Gates, a Caltrans seismic design expert, wrote a memo to Bill Jones, a department contracts official, noting that two other freeways in San Francisco--the China Basin Viaduct and the Central Viaduct of U.S. 101--contained the same vulnerable configuration of column connections or “hinges” as the Embarcadero.

The memo notes that Roberts had requested that these freeways be included in a $64-million program--known as Phase 2 and not yet begun--to strengthen about 700 bridges in the state that are supported by single columns. But the memo did not mention the doomed Nimitz Freeway.

“Maybe it was a lack of thought process,” said the sometimes wry Roberts, when asked why Caltrans did not include the Nimitz in Phase 2.

Phase 1 of the earthquake strengthening plan involved tying highway bridge roadbed sections together with steel cables and was recently finished. Phase 2 is to begin in January.

Caltrans officials say the Nimitz and other bridges supported by double-column structures were to be strengthened against earthquakes in a Phase 3, when the technology is developed.

The Aug. 21 memo was released by Caltrans on Thursday and seemed to catch Roberts by surprise. He deferred questions on the subject until Friday’s news conference, saying that he had never seen the memo.

Even if the Nimitz had been identified as containing similar design problems as the three San Francisco bridges, it seems highly unlikely that anything would have been done to strengthen the structure before the earthquake.

At the time of the earthquake, Caltrans had not yet begun any of the work recommend by the panel of engineers to strengthen the columns of the three San Francisco bridges. Roberts said these structures are the only freeways in the state similar in design to the Nimitz.

The three San Francisco freeways suffered damage but did not collapse and Caltrans is now shoring up the columns.

Stephen Mahin, a UC Berkeley professor of civil engineering who took part in the Aug. 1 review of the Embarcadero Freeway, told The Times that the configurations of the so-called “hinges” that made the Embarcadero vulnerable are similar to those on the Nimitz, but added that there are important differences in the two structures. He said that the type of strengthening needed for the Embarcadero probably would not have saved the poorly reinforced column joints that are believed to have failed on the Nimitz.

Nevertheless, the structure could have been saved with existing technology, according to George W. Housner, the prestigious expert on earthquake engineering whom Gov. Deukmejian appointed Thursday to lead an investigation into the Nimitz disaster. He said in an interview Thursday that engineers have the technology to buttress freeways to withstand earthquakes as strong as an 8.6 jolt. The Oct. 17 quake registered 7.1 and was centered 50 miles from the Nimitz.

“It would depend on each particular case how difficult it is and how much has to be done,” he said of strengthening freeway bridges. “I’m sure it can be done. There is no question in my mind about that.”

On Thursday, Roberts had said that the program to tie roadbed sections of freeways together with steel cables to prevent them from coming apart during earthquakes might have contributed to the magnitude of the Nimitz collapse by concentrating the full force of the quake on all the structure’s columns at once. But he said on Friday that the tie-down system on the state’s bridges may have saved many more lives than were lost in the Nimitz disaster by preventing bridge failures in other locations.

Roberts said that the department will begin conducting an inspection of highway bridges throughout Southern California. Many of the bridges already slated for earthquake-resistance work are in the Los Angeles area, although none are similar in design to the Cypress Viaduct, which collapsed on the Nimitz.

“We’re getting all kinds of calls. People are concerned,” Roberts said. “What we will do, I am certain, is do an expedited review of all the bridges in the Southern California area where we feel there is some concern.”

The analysis will have to wait at least several weeks because most of the Caltrans maintenance engineers able to carry out the work are still in the San Francisco Bay Area helping with bridge inspections and repairs.

The department has already begun examining a double-decker section of the Santa Monica Freeway where it crosses the Los Angeles River, as well as reviewing plans for double-decking a 2.6-mile section of the Harbor Freeway.

Times staff writer Daniel M. Weintraub in Los Angeles contributed to this story.

STORIES, PICTURES: A28-A33.